Understanding the process of how cells decide when to grow, when to divide and which pathway of differentiation to follow is fundamental to a successful analysis of normal embryonic development as well as pathology. In this proposal we consider growth regulation and cell differentiation from several perspectives and with several experimental systems. Growth control, cell differentiation and intracellular signaling are approached from a variety of biochemical, molecular biological, and genetic approaches in yeast, Drosophila, nematodes, and Xenopus. It now seems likely that common regulatory mechanisms will be found in many different systems; in each we will utilize its particular experimental strengths for the study of these mechanisms. These studies have already identified important cell biological components and processes such as the importance in cellular development of membrane receptors and signaling, oncogenes, growth factors, transcriptional and translational control. The overall goal of this research is to identify some of the most significant processes for cell determination and growth control in eukaryotic organisms and to elucidate some of the fundamental mechanisms underlying these processes.